The field of the invention is, in lines for processing metal strips (for example rolling mills), that of rotary shearing devices used to fragment edge scrap into multiple pieces.
During operations of processing a metal strip, it is known to cut the edges of the metal strip in order to get the strip to the desired width. This operation is conventionally carried out via pairs of cutting discs that cut the strip during the travel of said strip, near the edges, in the direction in which the strip moves forward.
The strip, cut to size, continues moving forward on the processing line, while each section of strip cut off, called “edge scrap”, is diverted and guided out of the line. Document U.S. Pat. No. 2,417,556 teaches such a cutting device having discs.
This strip is waste that can be wound onto a mandrel or compacted when too much strip accumulates.
Another solution is to fragment this continuous waste into multiple pieces during the travel of said waste, via a rotary shearing device.
A person skilled in the art thus knows numerous rotary shearing devices for fragmenting edge scrap.
For example, document U.S. Pat. No. 3,799,020 discloses a shearing device comprising a drum provided on the circumference with a plurality of blades and with a stationary counter-blade intended to successively cooperate in the shearing with the blades of the drum during the rotation of said drum. FIG. 1 of this prior art illustrates the edge scrap that is diverted from the line and fragmented continuously between the blades of the drum, which rotates, and the counter-blade, which is stationary.
The invention relates, however, more particularly to the shearing device having two counter-rotating drums.
In this type of shearing device, as taught by document U.S. Pat. No. 4,004,479, two counter-rotating drums are positioned facing each other, a drive device connecting the drums and controlling the speed of rotation of said drums. The drums are provided with blades (or “knives”) positioned in pairs, respectively. The blades of each of the drums are arranged, transversely to the drum, in order to work in shearing in pairs and fragment the strip while the strip is driven between the drums.
In order to obtain a good cut, the rotations of the drums must be precisely synchronised, which allows the cutting clearance, in particular circumferential, between the blades of the pair to be controlled during shearing. For this purpose and as taught by document U.S. Pat. No. 4,004,479, it is known to synchronise the rotations of the drums via gears without any play (“anti-backlash gears”) linking the rotation of the shafts of the drums.
The cutting clearance between the blades of the same pair during the shearing is conventionally determined on the basis of the thickness of the strip to be cut. The thinner the strip, the more this cutting clearance must be reduced. In practice, a person skilled in the art respects the rule of 1/10, namely that the cutting clearance between blades is determined as 1/10 of the strip thickness to be cut.
In the shearing device having counter-rotating drums taught by document U.S. Pat. No. 4,004,479, the blades are substantially parallelepiped-shaped bars regularly distributed on the circumference of the drum and each oriented transversely to the drum. The cutting edges of the blades are rectilinear and substantially parallel to the axis of rotation of the drum.
Such a device, however, is not totally satisfactory because said device causes impacts and not progressive cutting of the edge scrap.
In order to obtain progressive cutting of the edge scrap, and thus substantially limit the noise of the cutting, a person skilled in the art knows, for example from document DE1117358, to orient the blades at an angle with respect to the axis of rotation of the drum. In other words, the longitudinal direction of each blade (and of the cutting edge thereof) is no longer parallel to the axis of the drum but inclined with respect to said axis. Moreover, the blades belonging to the two drums have opposite diagonal orientations. Thus, the shearing begins locally at the two longitudinal ends of the blades of the pair and moves along the blades up to the two opposite longitudinal ends, which allows the noise of cutting to be reduced quite substantially.
Moreover, a person skilled in the art knows that the cutting diameter (namely, double the distance between the cutting edge of each blade and the axis of rotation of the drum) can only be, in the devices of the prior art, very slightly greater than the centre-to-centre distance between the two drums, otherwise, during the rotation of the drums, contacts between the cutting edges of the blades and the overlapping faces of said blades may occur, causing premature wear to the cutting edges of the blades.
When the cutting diameter is greater than the centre-to-centre distance by too much, given the cutting clearance that must be respected, there is too much overlapping between the blades (of the same pair) to avoid having these blades impact each other during the shearing.
When the blades are inclined with respect to the axis of the drum, in such a way as to obtain progressive cutting, as taught by document DE 1117358, it is therefore, according to the known prior art, necessary to machine the cutting edge in a curved way in such a way that, as much as possible, the radius separating the axis of the drum and the cutting edge be constant over the length of this cutting edge. It is no longer possible to have a rectilinear cutting edge in that this cutting edge would be, at the longitudinal ends of the blade, locally, at a radius much greater than the radius of the cutting edge, locally, in the median zone of the blade. At these longitudinal ends, there would therefore be too much overlapping between the blades of the drums to avoid interference between the cutting edges of these rectilinear blades and the overlapping faces of the opposite blades.
Conventionally, such curved machining of the cutting edge of the blades is carried out using blades that are substantially parallelepiped-shaped, previously mounted on each of the drums, which are necessarily removable drums that can be dissociated from the respective rotating shafts thereof in order to allow the curved machining operation to be carried out.
The parallelepiped-shaped blades/drum assembly is then removed from the shearing device and positioned on a machining station. On this machining station, the cutting edges of the blades are reground in a curved manner. Once this machining work is finished, the drum is removed from the machining station in order to be mounted on the rotating shaft of the shearing device.
As the blades wear, it is possible to use wedges between the blades and the drum in order to make the blades of the drum stick out more and to carry out a new regrinding of the blades, along a curved trajectory, according to the aforementioned machining procedure.
Such prior art conventionally requires having an additional set of drums in order to allow the regrinding of the blades, with the goal of not having to stop the rolling mill for too long during these maintenance periods.
An intrinsic disadvantage of such a device is caused by the removable nature of the drums with respect to the respective shafts thereof. It is not rare to note a defect in the positioning of the drum on the shaft of said drum, which inevitably leads to errors in the cutting clearances and thus to cutting defects.
From document FR 2 640 174, a shearing device having two counter-rotating drums is again known. Like the previous document, the blades are not parallel to the axis of rotation of the drum, but at an angle with respect to said axis, in such a way as to produce progressive shearing of the waste.
Unlike the previous document, the device of document FR 2 640 174 involves the use of curved blades machined along a predetermined radius of curvature before said blades are mounted on the drum of said blades.
Each blade is characterised by convex outer faces and flat lateral faces, and four (curved) cutting edges formed at the intersections between the lateral faces and the two convex outer faces. When one of the cutting edges is worn, the blade is removed from the drum and remounted in a different position in order to expose one of the other cutting edges.
The prior art of shearing devices having counter-rotating drums and progressive cutting, taught in particular by document FR 2 640 174 or DE 1117358, are, to the knowledge of the applicant, exclusively reserved for fragmenting scrap from products having large thicknesses, typically greater than 1 mm, and having high yield strengths, typically greater than 300 MPa.
This is explained by the fact that, in these devices of the prior art, the cutting diameter (namely, double the distance between the cutting edge of each blade and the axis of rotation of the drum) can only be very slightly greater than the centre-to-centre distance between the two drums, otherwise, premature wear of the cutting edges may occur.
This size constraint implies little overlapping between the blades in order to prevent the blades from impacting each other during the shearing.
For products having large thicknesses and high yield strengths, such devices allow cutting via brittle fracturing of the product, without there being any overlapping of the blades and thus without the risk of impact between the blades, even with a small cutting clearance.
However, it is known that such devices are not suitable for thinner products, namely less than 0.3 mm, and/or soft products, which have significant coefficient of elongation at rupture products (>20%), in that these products are inserted into the clearance between blades without brittle fracturing of the product taking place, the overlapping thus being insufficient to allow the product to be cut via tearing.
Moreover, and for certain devices of the type in document DE1117358, the blades are mounted on the respective drum thereof via radial screws and wedges. The clamping of these wedges via screwing must be progressive and precise, conventionally via a predetermined procedure, otherwise the removable drum may be ovalised, such an ovalisation modifying the cutting clearance and leading to cutting defects.
In the prior art of shearing machines having counter-rotating drums, a shearing machine, the two blades of which, carried by the drums, respectively, have rectilinear cutting edges, is also known from document BE 490 046, dating to 1949. In this document, the rectilinear cutting edge (called cutting edge) of each blade has an axis strictly parallel to the axis of rotation of the corresponding drum, which carries the blade. This document teaches inclining the blades with respect to the radial plane passing through the cutting edge in order to allow clean shearing. Thus, and as illustrated in FIG. 3 of document BE 490 046, for each drum, the plane passing through the overlapping face of the blade never intersects the axis of rotation of the corresponding drum.
In FIG. 4, this document also teaches reducing the impacts during the shearing by inclining the axis of rotation O1-O1 of the first drum with respect to the axis of rotation O2-O2 of the second drum, while the rectilinear cutting edge (called cutting edge) of each blade conserves an axis strictly parallel to the axis of rotation of the corresponding drum, which carries the blade. According to the observations of the inventors, such an inclination between the axes of rotation of the two drums, with the goal of reducing impacts, can only be very slight and does not allow progressive shearing to be obtained as taught by document DE1117358, when the blades of the pair are each inclined by an angle with respect to the axis of rotation of the corresponding drum thereof, the blades of the pair carried by the two drums having opposite diagonal orientations. According to the observations of the inventor, such a shearing machine according to this prior art document BE490046 does not allow fractioning at a high speed, and contrary to the shearing machines of prior art documents DE1117358 and FR 2640174.
A shearing machine having counter-rotating drums and in which the blades of the pair, carried by the two drums, have a rectilinear cutting edge (called cutting edges, labelled 1 and 2) is also known from document FR 2306773. According to the description of this prior art document, the axes of rotation of the drums labelled “xx” and “yy” are parallel to each other.
According to this prior art document, each of the cutting edges, labelled 1 or 2, is contained in a plane, labelled 3 or 4, that passes through the axis of rotation of the drum xx or yy. Moreover, the edges are inclined by the same angle with respect to the shared direction of the axes of rotation of the drums, with the goal of obtaining a progressive cut.
Here again, and according to the observations of the inventor, such a blade inclination along an axis of rotation perpendicular to the radial plane can only be very minimal in comparison to the inclination of the blades as taught by document DE 1117358 or FR 2640174, in which the blades carried by the drums have opposite diagonal orientations. A shearing machine as taught by document FR 2306773 does not allow the progressive cutting of the shearing machines of documents DE 1117358 and FR 2640174 to be obtained. In document DE 1117358 or FR 2640174, the inclination that allows the progressive cutting is obtained substantially via a rotation of the blade about an axis of rotation substantially radial and perpendicular to the axis of rotation, while in document FR 2306773, the inclination is obtained by a rotation of the blade about an axis of rotation perpendicular to the radial plane.
When the blades are inclined according to the teaching of document DE1117358, the rectilinear edge or cutting edge of the blades and the axis of rotation of the drum are not coplanar: the edge cannot be contained in a plane passing through the axis of rotation of the drum as taught by document FR2306773. According to the observations of the inventor, and like the previous document, such a shearing machine according to this prior art document FR2306773 does not allow fractioning at a high speed, and contrary to the shearing machines of prior art documents DE1117358 and FR 2640174.